Pro OpenGL ES for iOS

316 CHAPTER 10: OpenGL ES 2, Shaders, and...^

„ Besides binding the attributes to named entities in the shaders, you

can also do the same with uniforms, as demonstrated in lines 6 and 7.

Remember that uniforms are merely values passed from the calling

program. (They differ from attributes in that attributes are mapped

one-to-one with each vertex.) In this case, we are supplying two

matrices and naming them modelViewProjectionMatrix and

normalMatrix. Looking again in the vertex shader, you can see the

following:

uniform mat4 modelViewProjectionMatrix;

uniform mat3 normalMatrix;

„ Lines 7ff support a memory optimization quark. Once linked, the

shader code is copied into the program, so the shader objects as we

have them are no longer needed. Since they use reference counts,

glDetachShader() serves to decrease the count by one, and, of

course, when 0, they can be safely deleted.

„ As a side effect, if you change the shader in anyway, it will have to be

relinked before the changes take effect. And in case you may have to

relink things, the driver may hold onto some cached information to use

later. Otherwise, the detach/delete process can aid the driver in

reusing the cached memory.

As you can see, the actual calls required are pretty minimal, but Apple’s demo includes

all of the error handling as well, which is why it was retained.

Now with that out of the way, we can look at the two shaders. Listing 10-5 is the vertex

shader, Shader.vsh. Note that the shaders pairs share the same prefix, with the vertex

shader having a suffix of vsh while the fragment shader uses fsh.

Listing 10-5. The Demo’s Vertex Shader

attribute vec4 position; //1

attribute vec3 normal;

varying lowp vec4 colorVarying; //2

uniform mat4 modelViewProjectionMatrix; //3

uniform mat3 normalMatrix;

void main()

{

vec3 normalDirection = normalize(normalMatrix * normal); //4

vec3 lightPosition = vec3(0.0, 0.0, 1.0); //5

vec4 diffuseColor = vec4(0.4, 0.4, 1.0, 1.0); //6

float nDotVP = max(0.0, dot(eyeNormal, normalize(lightPosition))); //7

colorVarying = diffuseColor * nDotVP; //8

gl_Position = modelViewProjectionMatrix * position; //9

}